Antennas have become essential components of most modern communications and radar systems. One benefit of these antennas is the ability for their beams to be easily scanned or re-configured, as required by the system. Another benefit of these antennas is their ability to generate more than one beam simultaneously.
As operating frequencies rise, array antennas are desirably constructed as smaller devices. This is because the required spacing between radiating elements within the antenna is typically a function of wavelength. There is a strong technical incentive, therefore, to make these antennas compact.
In modern satellite services, each service generally covers a different frequency range, different polarization, and different space allocations. Consumers are interested in addressing these different services without having to use a different antenna to access each service.
Conventional solutions for designing a single antenna capable of communicating with various services entail the use of expensive phase shifters, typically using Monolithic Microwave Integrated Circuits (MIMIC) circuits. There is, therefore, also a strong commercial incentive, especially in the newly developing millimeter-wave LMDS and satellite services, to minimize size and cost.
As phased array antennas become smaller, however, it becomes more difficult to generate, distribute, and control the power needed to drive these devices.
In addition to the size constraints imposed on antennas by modern communications systems, higher frequency systems require the development of lower-loss power distribution techniques. Many RF systems operating in the millimeter-wave range, such as vehicular and military radars and various types of communications systems, require the distribution and collection of RF signals with minimal attenuation in order to maintain high efficiency and sensitivity. Conventional power distribution techniques, however, have associated problems which prevent this desired balance between efficiency, sensitivity and attenuation.
Planar antennas have been known to be very difficult to design, as they have historically used EM coupling from a buried feed network to radiating elements mounted on the surface of the antenna. In particular, EM waves are difficult to direct, and energy can leak in various directions, degrading the isolation between the feed network and the radiating elements. This problematic scenario is compounded if multiple signals having different polarizations are fed to the radiating elements, each polarization having its own feed network in a multi-level environment.